Sublimating apparatus



1941- H; J. M. VAN EMBDEN 2,252,052

SUBLIMATING APPARATUS Filed Oct. 6, 1939 Jill/U, min-Z5689;

Patented Aug. 12, 1941 SUBLIMATING APPARATUS Hendrik Johannes Meerkamp van Embden, Eindhoven, Netherlands, assignor, by mesne assignmcnts, to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application October 6, 1939, Serial No. 298,330 In Great Britain October 17, 1938 1 Claim.

My invention relates to an apparatus for sublimating materials under low pressure.

As is well known, many materials, for example iodine, and the light metals such as magnesium, beryllium and the like, can be separated by sublimation from ores in which they are contained in a chemically bound condition. For this purpose the ores together with a reducing agent are placed in a suitable apparatus and are heated at a temperature of more than 1000 C. in an atmosphere of low pressure, for instance 2 cms. of mercury or less. As a result the metal is vaporized immediately by the high temperature and low pressure, and the vapors thereof pass to colder portions, i. e. condensing portions, of the apparatus and condense on the surface thereof to form a sublimate.

If the temperature of the condensing portions of the apparatus is so far below the condensation temperature of the vapor that the sublimate crystallizes too rapidly, the sublimate will be in a very finely divided form. This has the disadvantage that when the apparatus is opened to remove the sublimate, the sublimate, due to its finely-divided state, will be readily oxidized by air. For this reason there will be losses due to oxidation and the sublimate may even be set on fire.

To overcome the above-mentioned disadvantages it has been proposed to regulate the-temperature of the condensing portion of the apparatus by heating the same with a stream of hot furnace gases. However, I have found that such methods are not satisfactory because it is impossible to obtain an exact regulation of the temperature of the condensing parts whose temperature depends to a large degree upon the amount of the sublimate being condensed and upon the composition of the fuel.

The object of my invention is to overcome the above difiiculties and for this purpose I provide an apparatus in which substantially all the heat removed from the condensing portion is transthereof will be maintained above that tempera- I ture at which the vapors condense crystallized form.

The apparatus of the invention ensures a very in a coarse exact regulation of the temperature of the condensing portion because any increase inits temperature caused by an increase in the amount of the sublimate being condensed thereon will be automatically compensated by an increase in the amount of heat radiated. Similarly, a decrease in the temperature will be compensated by a decrease in the radiation. v

In one embodiment of my invention I provide a cooling jacket which has a surface opposing the surface of the condensing portion with a narrow intermediate space, which is evacuated. In this case the dissipation of heat from the condensing member to the cooling system is retarded and the condensing member gives off its heat only at higher temperatures.

In order that the invention may be clearly understood and readily carried into effect I shall describe the same in more detail with reference to the accompanying drawing in which the single figure is a sectionized side view of an apparatus according to the invention.

The apparatus shown in the drawing comprises a crucible of a refractory non-conductive material which contains a charge 2. The charge 2 includes the ore of the metal to be sublimated, a reducing agent, and, if it is non-conductive, also a conducting material. A dome-shaped metal cover l2, for instance of copper, rests upon the top of crucible l and is provided at its top with an opening l3 which allows for the removal of the non-condensing gases.

The crucible I is supported on a base plate 5, of stoneware, and a vacuum-tight cylinder 6, for instance of porcelain, has its lower flanged end resting upon the plate 5 to form a hermeticallytight joint therewith. The charge I is heated by a high-frequency field generated by a winding 8 surrounding the cylinder 6.

Resting upon the top flange of cylinder 8 so as to form a hermetically-tight joint therewith is a double-walled cooling jacket 1 provided on its upper end with a flanged tubular extension 15 forming an outlet l0. As the jacket 'I is located outside the high-frequency field generated by winding' 8 it may be made of metal. The'jacket l is filled with water 9 to maintain its temperature low enough to prevent warping and to take up the heat produced by condensation of the vapor and radiated from the outer surface 3 of the cover [2 through space 4 to the opposing surface it of the jacket'l. This jacket is provided with an outlet passage I8 for the removal of steam formed by the heating of the jacket.

Connected to the extension I5 is a tube ll connected to a vacuum pump I? whereby a pressure of about 20 ms. of mercury is maintained within the apparatus.

'When the charge i is heated by the high-frequency field, gases are disengaged therefrom. At the low pressure used, the condensation point of the gases of the material to be Sublimated is higher than that of the cover i2 and consequently these gases condense when coming into contact with the cover and the sublimate forms thereon. The other gases, which do not condense under these conditions, pass through opening i3, the'outlet iii and tube ii to the vacuum pump.

To obtain a high efficiency it is necessary. that as much as possible of the gases of the sublimated material should be condensed and that only the non-condensing gases resulting from leakage or impurities in the charge should pass through opening i3. Therefore I locate the opening it present case is as far as possible from the crucible i. The outlet iii is located opposite the opening it in order that the non-condensing gases can be removed by the shortest route.

The opening pressure on both sides of the cover I2 whose wall is made thin to allow for the rapid transfer of heat and therefore is not capable of withstanding high pressure differences.

. When the gases and vapors given oii by the charge i condense upon the cover l2, a considerable amount of heat energy is imparted thereto. This heat will not be conducted to the crucible i because the crucible is at a high temperature.

Thus substantially the only way in which the heat may be removed from the cover 12 is by radiation through the space 4 between surfaces 3 and M to the cooling jacket I; the other means of heat transmission being comparatively small.

As the total energy radiated from the cover I2 is proportional to the fourth power of its absolute temperature, an increase in the temperature of the cover results immediately in a more intense radiation. As a result the temperature of the cover can be maintained substantially constant. This is of thegreatest importance for the condensation of the sublimate so that the actual temperature of the cover may fluctuate only between narrow limits.

The temperature of the cover is a function of the intensity of the radiation and this intensity can be increased or decreased by means which are known per se. For example to increase the it also serves to equalize the intensity or radiation the outer surface of the cover may be provided with a coat of dead-black paint i6, or cooling ribs and the like may be provided.

If it is found that the temperature of the cover i2 is temporarily too low, for example is slow in reaching the desired value at the beginning of the process, it can be rapidly increased to the desired value by causing part of the high-frequency field to extend through a portion of the cover. For this purpose the winding 8 may be placed higher so as to surround the lower part of cover i2. However, I have found that this is generally unnecessary, because the heat developed by the condensation of the sublimate is usually sumcient. Therefore, I generally locate the cover outside the high-frequency field, as shown.

In manufacturing pure metallic magnesium I use a mixture of magnesite and a suitable reduc tion agent. At a pressure of 10 mm. mercury the charge of the crucible is heated by means of high frequency induction. For sublimating magnesium in a coarse crystalline form the temperature of the cover should be maintained between 300 C. and 600 C. and if that temperature were allowed to fall below about 200 C. the magnesium sublimate would be in a finely divided state, unsuitable for regular production.

I wish it to be understood that I do not wish to be limited to the exact details of construction shown and described, for obvious modifications will occur to a person skilled in the art.

What I claim is:

A vacuum sublimating apparatus. comprising a crucible of non-metallic material adapted to receive the material to be Sublimated, means to produce high-frequency current for heating the material to be Sublimated, a dome-shaped metal cover on said crucible and serving as a condensing member for the vapors of the sublimate, said cover being tightly jointed to the crucible and being provided with an outlet opening, the spaces within the cover and crucible being connected by a passageway having a cross-sectional area approximately the same as the area of the free surface of the charge within the crucible, and means to remove heat from said cover substantially only by radiation, said means comprising a heat-receiving member surrounding said cover with an intermediate space, and a device for producing a low pressure within said space.

HENDRIK JOHANNES MEERKAMP VAN EMBDEN. 

